Again, the EH101 and I believe the Aw139 and the EC225 family do actually HAVE a 30 minute dry run capability, designed, proven and certified. That means you fill the box, drain it out and run at flight powers for 30 minutes, with authority wintesses.
dangermouse,
I agree that all rotorcraft drivetrains should have a demonstrated run dry capability. I also support the US AATD's push for 60 minutes instead of the current 30 minute standard. But having said that, engineering an MRGB with even a 30 minute run dry capability is pretty difficult to do. It can also add quite a bit of expense and complexity, since it usually involves things like multiple, redundant lube system components and exotic high-temp tolerant gear and bearing steels.
In a typical multi-engine MRGB, the lube system is by far the most complex element. Since the lube oil is the primary method of cooling the gears and bearings, once oil flow is interrupted the gears and bearings will quickly build up heat, lose temper strength, and structurally fail.
The problem is made worse when there are multiple, high power engines. The achilles heel of a gearbox like the S-92's is the input bevel gear set. Here you have 100% of engine power passing through a single spiral bevel gear mesh. The high transmitted power combined with the relatively lower efficiency of the spiral bevel gear mesh means this is the most likely point of failure with loss of lube.
As for analyzing and certifying a lube system catastrophic failure event as being "extremely remote", that would have been the result of a statistical reliability analysis and FMEA. The statistical failure rates for each component used in the reliability analysis should have been the same used throughout the industry. The first thing a good attorney would do is get a copy of that reliability analysis and nitpick every failure rate value used. With so many components in the lube system, even a very small change in each component reliability rate would be compounded into a very large change in the overall system reliability rate.
riff_raff